Due to the rising cost of liquid fuel (e.g. diesel fuel) and ever increasing restrictions on exhaust emissions, engine manufacturers have developed dual-fuel engines. An exemplary dual-fuel engine provides injections of a low-cost gaseous fuel (e.g. natural gas) through air intake ports of the engine's cylinders. The gaseous fuel is introduced with clean air that enters through the intake ports and is ignited by liquid fuel that is injected during each combustion cycle. Because a lower-cost fuel is used together with liquid fuel, cost efficiency may be improved. In addition, the combustion of the gaseous and liquid fuel mixture may result in a reduction of harmful emissions.
In these dual-fuel engines, particular attention may be directed to pressures, flow rates, and timing of the gaseous and liquid fuels injected into the cylinder. If these parameters are not tightly controlled, the engine may not perform as expected.
An exemplary control system for a dual-fuel engine is disclosed in U.S. Pat. No. 4,527,516 to Foster. In particular, the '516 patent discloses a dual-fuel engine that includes an inlet pipe connected at one end to a gas source and at an opposite end to the side of an engine cylinder via an inlet port. The '516 patent also includes an electronically controlled gas admission valve to control the timing of the gas entry into the cylinder via the inlet pipe. The gas admission valve controls a parameter of the gas flow to meet engine requirements, but does not rely on feedback for control purposes. Instead, the valve only includes feed-forward control to meet given fuel specifications.
Although perhaps adequate for some applications, the control system of the '516 patent may be less than optimal. In particular, because the control system only uses feed-forward control, it may not account for variations in environmental factors and/or aging factors that can have an effect on system performance.
The disclosed control system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.